Field of the Invention
The present inventions relate to synthetic proppants, ceramic proppants and polymeric derived ceramic proppants; methods for making these proppants; fracing fluids utilizing these proppants; and hydraulic fracturing methods with these proppants. In particular, the present inventions relate to proppants and hydraulic fracturing activities that utilize polymeric derived siloxane based ceramics. Thus, the present inventions further relate to treating wells, e.g., hydrocarbon producing wells, water wells and geothermal wells, to increase and enhance the production from these wells by siloxane based polymeric derived ceramic proppant hydraulic fracturing. Still more particularly, methods are provided for increasing the fluid conductivity between a subterranean formation containing a desired natural resource, e.g., natural gas, crude oil, water, and geothermal heat source, and a well or borehole to transport the natural resource to the surface or a desired location or collection point for that natural resource.
In the production of natural resources from formations within the earth a well or borehole is drilled into the earth to the location where the natural resource is believed to be located. These natural resources may be a hydrocarbon reservoir, containing natural gas, crude oil and combinations of these; the natural resource may be fresh water; it may be a heat source for geothermal energy; or it may be some other natural resource that is located within the ground.
These resource-containing formations may be a few hundred feet, a few thousand feet, or tens of thousands of feet below the surface of the earth, including under the floor of a body of water, e.g., below the sea floor. In addition to being at various depths within the earth, these formations may cover areas of differing sizes, shapes and volumes.
Unfortunately, and generally, when a well is drilled into these formations the natural resources rarely flow into the well at rates, durations and amounts that are economically viable. This problem occurs for several reasons, some of which are well understood, others of which are not as well understood, and some of which may not yet be known. These problems can relate to the viscosity of the natural resource, the porosity of the formation, the geology of the formation, the formation pressures, and the perforations that place the production tubing in the well in fluid communication with the formation, to name a few.
Typically, and by way of general illustration, in drilling a well an initial borehole is made into the earth, e.g., the surface of land or seabed, and then subsequent and smaller diameter boreholes are drilled to extend the overall depth of the borehole. In this manner as the overall borehole gets deeper its diameter becomes smaller; resulting in what can be envisioned as a telescoping assembly of holes with the largest diameter hole being at the top of the borehole closest to the surface of the earth.
Thus, by way of example, the starting phases of a subsea drill process may be explained in general as follows. Once the drilling rig is positioned on the surface of the water over the area where drilling is to take place, an initial borehole is made by drilling a 36″ hole in the earth to a depth of about 200-300 ft. below the seafloor. A 30″ casing is inserted into this initial borehole. This 30″ casing may also be called a conductor. The 30″ conductor may or may not be cemented into place. During this drilling operation a riser is generally not used and the cuttings from the borehole, e.g., the earth and other material removed from the borehole by the drilling activity are returned to the seafloor. Next, a 26″ diameter borehole is drilled within the 30″ casing, extending the depth of the borehole to about 1,000-1,500 ft. This drilling operation may also be conducted without using a riser. A 20″ casing is then inserted into the 30″ conductor and 26″ borehole. This 20″ casing is cemented into place. The 20″ casing has a wellhead secured to it. (In other operations an additional smaller diameter borehole may be drilled, and a smaller diameter casing inserted into that borehole with the wellhead being secured to that smaller diameter casing.) A BOP (blow out preventer) is then secured to a riser and lowered by the riser to the sea floor; where the BOP is secured to the wellhead. From this point forward all drilling activity in the borehole takes place through the riser and the BOP.
For a land based drill process, the steps are similar, although the large diameter tubulars, 30″-20″ are typically not used. Thus, and generally, there is a surface casing that is typically about 13⅜″ diameter. This may extend from the surface, e.g., wellhead and BOP, to depths of tens of feet to hundreds of feet. One of the purposes of the surface casing is to meet environmental concerns in protecting ground water. The surface casing should have sufficiently large diameter to allow the drill string, product equipment such as ESPs and circulation mud to pass through. Below the casing one or more different diameter intermediate casings may be used. (It is understood that sections of a borehole may not be cased, which sections are referred to as open hole.) These can have diameters in the range of about 9″ to about 7″, although larger and smaller sizes may be used, and can extend to depths of thousands and tens of thousands of feet. Inside of the casing and extending from a pay zone, or production zone of the borehole up to and through the wellhead on the surface is the production tubing. There may be a single production tubing or multiple production tubings in a single borehole, with each of the production tubing endings being at different depths.
Typically, when completing a well, it is necessary to perform a perforation operation, and perform a hydraulic fracturing, or fracing operation. In general, when a well has been drilled and casing, e.g., a metal pipe, is run to the prescribed depth, the casing is typically cemented in place by pumping cement down and into the annular space between the casing and the earth. (It is understood that many different down hole casing, open hole, and completion approaches may be used.) The casing, among other things, prevents the hole from collapsing and fluids from flowing between permeable zones in the annulus. Thus, this casing forms a structural support for the well and a barrier to the earth.
While important for the structural integrity of the well, the casing and cement present a problem when they are in the production zone. Thus, in addition to holding back the earth, they also prevent the hydrocarbons from flowing into the well and from being recovered. Additionally, the formation itself may have been damaged by the drilling process, e.g., by the pressure from the drilling mud, and this damaged area of the formation may form an additional barrier to the flow of hydrocarbons into the well. Similarly, in most situations where casing is not needed in the production area, e.g., open hole, the formation itself is generally tight, and more typically can be very tight, and thus, will not permit the hydrocarbons to flow into the well. In some situations the formation pressure is large enough that the hydrocarbons readily flow into the well in an uncased, or open hole. Nevertheless, as formation pressure lessens a point will be reached where the formation itself shuts-off, or significantly reduces, the flow of hydrocarbons into the well. Also such low formation pressure could have insufficient force to flow fluid from the bottom of the borehole to the surface, requiring the use of artificial lift.
To address, in part, this problem of the flow of hydrocarbons (as well as other resources, e.g., geothermal) into the well being blocked by the casing, cement and the formation itself, openings, e.g., perforations, are made in the well in the area of the pay zone. Generally, a perforation is a small, about ¼″ to about 1″ or 2″ in diameter hole that extends through the casing, cement and damaged formation and goes into the formation. This hole creates a passage for the hydrocarbons to flow from the formation into the well. In a typical well, a large number of these holes are made through the casing and into the formation in the pay zone.
Generally, in a perforating operation a perforating tool or gun is lowered into the borehole to the location where the production zone or pay zone is located. The perforating gun is a long, typically round tool, that has a small enough diameter to fit into the casing or tubular and reach the area within the borehole where the production zone is believed to be. Once positioned in the production zone a series of explosive charges, e.g., shaped charges, are ignited. The hot gases and molten metal from the explosion cut a hole, i.e., the perf or perforation, through the casing and into the formation. These explosive-made perforations extend a few inches, e.g., 6″ to 18″ into the formation.
The ability of, or ease with which, the natural resource can flow out of the formation and into the well or production tubing (into and out of, for example, in the case of engineered geothermal wells, and some advanced recovery methods for hydrocarbon wells) can generally be understood as the fluid communication between the well and the formation. As this fluid communication is increased several enhancements or benefits may be obtained: the volume or rate of flow (e.g., gallons per minute) can increase; the distance within the formation out from the well where the natural resources will flow into the well can be increase (e.g., the volume and area of the formation that can be drained by a single well is increased, and it will thus take less total wells to recover the resources from an entire field); the time period when the well is producing resources can be lengthened; the flow rate can be maintained at a higher rate for a longer period of time; and combinations of these and other efficiencies and benefits.
Fluid communication between the formation and the well can be greatly increased by the use of hydraulic fracturing techniques. The first uses of hydraulic fracturing date back to the late 1940s and early 1950s. In general hydraulic fracturing treatments involve forcing fluids down the well and into the formation, where the fluids enter the formation and crack, e.g., force the layers of rock to break apart or fracture. These fractures create channels or flow paths that may have cross sections of a few micron's, to a few millimeters, to several millimeters in size, and potentially larger. The fractures may also extend out from the well in all directions for a few feet, several feet and tens of feet or further. It should be remembered that the longitudinal axis of the well in the reservoir may not be vertical: it may be on an angle (either slopping up or down) or it may be horizontal. For example, in the recovery of shale gas and oil the wells are typically essentially horizontal in the reservoir. The section of the well located within the reservoir, i.e., the section of the formation containing the natural resources, can be called the pay zone.
Typical fluid volumes in a propped fracturing treatment of a formation in general can range from a few thousand to a few million gallons. Proppant volumes can approach several thousand cubic feet. In general the objective of a proppant fracturing is to create and enhance fluid communication between the wellbore and the hydrocarbons in the formation, e.g., the reservoir. Thus, proppant fracturing techniques are used to create and enhance conductive pathways for the hydrocarbons to get from the reservoir to the wellbore. Further, a desirable way of enhancing the efficacy of proppant fracturing techniques is to have uniform proppant distribution. In this manner a uniformly conductive fracture along the wellbore height and fracture half-length can be provided. However, the complicated nature of proppant settling, and in particular in non-Newtonian fluids often causes a higher concentration of proppant to settle down in the lower part of the fracture. This in turn can create a lack of adequate proppant coverage on the upper portion of the fracture and the wellbore. Clustering of proppant, encapsulation, bridging, crushing and embedment are a few negative occurrences or phenomena that can lower the potential conductivity of the proppant pack, and efficacy of hydraulic fracture and the well.
The fluids used to perform hydraulic fracture can range from very simple, e.g., water, to very complex. Additionally, these fluids, e.g., fracing fluids or fracturing fluids, typically carry with them proppants; but not in all cases, e.g., when acids are used to fracture carbonate formations. Proppants are small particles, e.g., grains of sand, aluminum shot, sintered bauxite, ceramic beads, resin coated sand or ceramics, that are flowed into the fractures and hold, e.g., “prop” or hold open the fractures when the pressure of the fracturing fluid is reduced and the fluid is removed to allow the resource, e.g., hydrocarbons, to flow into the well.
In this manner the proppants hold open the fractures, keeping the channels open so that the hydrocarbons can more readily flow into the well. Additionally, the fractures greatly increase the surface area from which the hydrocarbons can flow into the well. Proppants may not be needed, or generally may not be used when acids are used to create a frac and subsequent channel in a carbonate rich reservoir, where the acids dissolve part or all of the rock leaving an opening for the formation fluids to flow to the wellbore.
Typically fracturing fluids consist primarily of water but also have other materials in them. The number of other materials, e.g., chemical additives used in a typical fracture treatment varies depending on the conditions of the specific well being fractured. Generally, a typical fracture treatment will use from about 2 to about 25 additives.
Generally the predominant fluids being used for fracture treatments in the shale formations are water-based fracturing fluids mixed with friction-reducing additives, e.g., slick water, or slick water fracs. Overall the concentration of additives in most slick water fracturing fluids is generally about 0.5% to 2% with water and sand making up 98% to 99.5% by weight. The addition of friction reducers allows fracturing fluids and proppant to be pumped to the target zone at a higher rate and reduced pressure than if water alone were used.
In addition to friction reducers, other such additives may be, for example, biocides to prevent microorganism growth and to reduce biofouling of the fractures; oxygen scavengers and other stabilizers to prevent corrosion of metal pipes; and acids that are used to remove drilling mud damage within the near-wellbore.
Further these chemicals and additives could be one or more of the following, and may have the following uses or address the following needs: diluted acid (≈15%), e.g., hydrochloric acid or muriatic acid, which may help dissolve minerals and initiate cracks in the rock; a biocide, e.g., glutaraldehyde, which eliminates bacteria in the water that produce corrosive byproducts; a breaker, e.g., ammonium persulfate, which allows a delayed break down of the gel polymer chains; a corrosion inhibitor, e.g., N,N-dimethyl formamide, which prevents the corrosion of pipes and equipment; a cross-linker, e.g., borate salts, which maintains fluid viscosity as temperature increases; a friction reducer; e.g., polyacrylamide or mineral oil, which minimizes friction between the fluid and the pipe; guar gum or hydroxyethyl cellulose, which thickens the water in order to help suspend the proppant; an iron control agent, e.g., citric acid, which prevents precipitation of metal oxides; potassium chloride, which creates a brine carrier fluid; an oxygen scavenger, e.g., ammonium bisulfite, which removes oxygen from the water to reduce corrosion; a pH adjuster or buffering agent, e.g., sodium or potassium carbonate, which helps to maintain the effectiveness of other additives, such as, e.g., the cross-linker; scale inhibitor, e.g., ethylene glycol, which prevents scale deposits in pipes and equipment; and a surfactant, e.g., isopropanol, which is used to increase the viscosity of the fracture fluid.
The composition of the fluid, the characteristics of the proppant, the amount of proppant, the pressures and volumes of fluids used, the number of times, e.g., stages, when the fluid is forced into the formation, and combinations and variations of these and other factors may be preselected and predetermined for specific fracturing jobs, based upon the formation, geology, perforation type, nature and characteristics of the natural resource, and formation pressure, among other things.
Generally, proppant transport inside a hydraulic fracture has two components when the fracture is being generated. The horizontal component is generally dictated by the fluid velocity and associated streamlines which help carry proppant to the tip of the fracture. The vertical component is generally dictated by the terminal particle settling velocity of the proppant particle in the fluid and is a function of proppant diameter and density as well as fluid viscosity and density. The terminal settling velocity, the fluid velocity, and thus the proppant transportation and deposit into the fractures can be further effected and complicated by the various phenomena and conditions present during the fracturing operation.
Proppant characteristics can play an important, if not critical role, in the success of the hydraulic fracturing operation. The proppants' ability to remain dispersed in the fluid and flow to the desired locations in the fractures, and to do so in a predictable manner to form packs, or assemblies of proppant in manners that enhance, rather than restrict, the flow of the natural resource being recovered is based upon its characteristics. The proppants must also be cost effective and preferably inexpensive to make and use, because of the large amounts of proppant material that is required for a fracturing job. Yet they must be strong enough to withstand the pressures of the formation and keep the fractures open. They must also be compatible with the various other components of the fracturing fluid, which for example, may include acids, such as HCl. Thus, for these and other reasons, the art has searched for, but prior to the present inventions has failed to find, a low density, highly uniform, inexpensive, and strong proppant.
Materials made of, or derived from, carbosilane or polycarbosilane (Si—C), silane or polysilane (Si—Si), silazane or polysilazane (Si—N—Si), silicon carbide (SiC), carbosilazane or polycarbosilazane (Si—N—Si—C—Si), siloxane or polysiloxanes (Si—O) are known. These general types of materials have great, but unrealized promise; and have failed to find large-scale applications or market acceptance. Instead, their use has been relegated to very narrow, limited, low volume, high priced and highly specific applications, such as a ceramic component in a rocket nozzle, or a patch for the space shuttle. Thus, they have failed to obtain wide spread use as ceramics, and it is believed they have obtained even less acceptance and use, if any, as a plastic material, e.g., cured but not pyrolized.
To a greater or lesser extent all of these materials and the process used to make them suffer from one or more failings, including for example: they are exceptionally expensive and difficult to make, having costs in the thousands and tens-of-thousands of dollars per pound; they require high and very high purity starting materials; the process requires hazardous organic solvents such as toluene, tetrahydrofuran (THF), and hexane; the materials are incapable of making non-reinforced structures having any usable strength; the process produces undesirable and hazardous byproducts, such as hydrochloric acid and sludge, which may contain magnesium; the process requires multiple solvent and reagent based reaction steps coupled with curing and pyrolizing steps; the materials are incapable of forming a useful prepreg; and their overall physical properties are mixed, e.g., good temperature properties but highly brittle.
As a result, although believed to have great promise, these types of materials have failed to find large-scale applications or market acceptance and have remained essentially scientific curiosities.
Related Art and Terminology
As used herein, unless specified otherwise, the terms “hydrocarbon exploration and production”, “exploration and production activities”, “E&P”, and “E&P activities”, and similar such terms are to be given their broadest possible meaning, and include surveying, geological analysis, well planning, reservoir planning, reservoir management, drilling a well, workover and completion activities, hydrocarbon production, flowing of hydrocarbons from a well, collection of hydrocarbons, secondary and tertiary recovery from a well, the management of flowing hydrocarbons from a well, and any other upstream activities.
As used herein, unless specified otherwise, the term “earth” should be given its broadest possible meaning, and includes, the ground, all natural materials, such as rocks, and artificial materials, such as concrete, that are or may be found in the ground.
As used herein, unless specified otherwise “offshore” and “offshore drilling activities” and similar such terms are used in their broadest sense and would include drilling activities on, or in, any body of water, whether fresh or salt water, whether manmade or naturally occurring, such as for example rivers, lakes, canals, inland seas, oceans, seas, such as the North Sea, bays and gulfs, such as the Gulf of Mexico. As used herein, unless specified otherwise the term “offshore drilling rig” is to be given its broadest possible meaning and would include fixed towers, tenders, platforms, barges, jack-ups, floating platforms, drill ships, dynamically positioned drill ships, semi-submersibles and dynamically positioned semi-submersibles. As used herein, unless specified otherwise the term “seafloor” is to be given its broadest possible meaning and would include any surface of the earth that lies under, or is at the bottom of, any body of water, whether fresh or salt water, whether manmade or naturally occurring.
As used herein, unless specified otherwise, the term “borehole” should be given it broadest possible meaning and includes any opening that is created in the earth that is substantially longer than it is wide, such as a well, a well bore, a well hole, a micro hole, a slimhole and other terms commonly used or known in the arts to define these types of narrow long passages. Wells would further include exploratory, production, abandoned, reentered, reworked, and injection wells. They would include both cased and uncased wells, and sections of those wells. Uncased wells, or section of wells, also are called open holes, or open hole sections. Boreholes may further have segments or sections that have different orientations, they may have straight sections and arcuate sections and combinations thereof. Thus, as used herein unless expressly provided otherwise, the “bottom” of a borehole, the “bottom surface” of the borehole and similar terms refer to the end of the borehole, i.e., that portion of the borehole furthest along the path of the borehole from the borehole's opening, the surface of the earth, or the borehole's beginning. The terms “side” and “wall” of a borehole should to be given their broadest possible meaning and include the longitudinal surfaces of the borehole, whether or not casing or a liner is present, as such, these terms would include the sides of an open borehole or the sides of the casing that has been positioned within a borehole. Boreholes may be made up of a single passage, multiple passages, connected passages, (e.g., branched configuration, fishboned configuration, or comb configuration), and combinations and variations thereof.
As used herein, unless specified otherwise, the term “advancing a borehole”, “drilling a well”, and similar such terms should be given their broadest possible meaning and include increasing the length of the borehole. Thus, by advancing a borehole, provided the orientation is not horizontal and is downward, e.g., less than 90°, the depth of the borehole may also be increased.
Boreholes are generally formed and advanced by using mechanical drilling equipment having a rotating drilling tool, e.g., a bit. For example, and in general, when creating a borehole in the earth, a drilling bit is extending to and into the earth and rotated to create a hole in the earth. To perform the drilling operation the bit must be forced against the material to be removed with a sufficient force to exceed the shear strength, compressive strength or combinations thereof, of that material. The material that is cut from the earth is generally known as cuttings, e.g., waste, which may be chips of rock, dust, rock fibers and other types of materials and structures that may be created by the bit's interactions with the earth. These cuttings are typically removed from the borehole by the use of fluids, which fluids can be liquids, foams or gases, or other materials know to the art.
The true vertical depth (“TVD”) of a borehole is the distance from the top or surface of the borehole to the depth at which the bottom of the borehole is located, measured along a straight vertical line. The measured depth (“MD”) of a borehole is the distance as measured along the actual path of the borehole from the top or surface to the bottom. As used herein unless specified otherwise the term depth of a borehole will refer to MD. In general, a point of reference may be used for the top of the borehole, such as the rotary table, drill floor, well head or initial opening or surface of the structure in which the borehole is placed.
As used herein, unless specified otherwise, the term “drill pipe” is to be given its broadest possible meaning and includes all forms of pipe used for drilling activities; and refers to a single section or piece of pipe. As used herein the terms “stand of drill pipe,” “drill pipe stand,” “stand of pipe,” “stand” and similar type terms should be given their broadest possible meaning and include two, three or four sections of drill pipe that have been connected, e.g., joined together, typically by joints having threaded connections. As used herein the terms “drill string,” “string,” “string of drill pipe,” string of pipe” and similar type terms should be given their broadest definition and would include a stand or stands joined together for the purpose of being employed in a borehole. Thus, a drill string could include many stands and many hundreds of sections of drill pipe.
As used herein, unless specified otherwise, the terms “workover,” “completion” and “workover and completion” and similar such terms should be given their broadest possible meanings and would include activities that take place at or near the completion of drilling a well, activities that take place at or the near the commencement of production from the well, activities that take place on the well when the well is a producing or operating well, activities that take place to reopen or reenter an abandoned or plugged well or branch of a well, and would also include for example, perforating, cementing, acidizing, fracturing, pressure testing, the removal of well debris, removal of plugs, insertion or replacement of production tubing, forming windows in casing to drill or complete lateral or branch wellbores, cutting and milling operations in general, insertion of screens, stimulating, cleaning, testing, analyzing and other such activities.
As used herein, unless specified otherwise, the terms “formation,” “reservoir,” “pay zone,” and similar terms, are to be given their broadest possible meanings and would include all locations, areas, and geological features within the earth that contain, may contain, or are believed to contain, hydrocarbons.
As used herein, unless specified otherwise, the terms “field,” “oil field” and similar terms, are to be given their broadest possible meanings, and would include any area of land, sea floor, or water that is loosely or directly associated with a formation, and more particularly with a resource containing formation, thus, a field may have one or more exploratory and producing wells associated with it, a field may have one or more governmental body or private resource leases associated with it, and one or more field(s) may be directly associated with a resource containing formation.
As used herein, unless specified otherwise, the terms “conventional gas”, “conventional oil”, “conventional”, “conventional production” and similar such terms are to be given their broadest possible meaning and include hydrocarbons, e.g., gas and oil, that are trapped in structures in the earth. Generally, in these conventional formations the hydrocarbons have migrated in permeable, or semi-permeable formations to a trap, or area where they are accumulated. Typically, in conventional formations a non-porous layer is above, or encompassing the area of accumulated hydrocarbons, in essence trapping the hydrocarbon accumulation. Conventional reservoirs have been historically the sources of the vast majority of hydrocarbons produced. As used herein, unless specified otherwise, the terms “unconventional gas”, “unconventional oil”, “unconventional”, “unconventional production” and similar such terms are to be given their broadest possible meaning and includes hydrocarbons that are held in impermeable rock, and which have not migrated to traps or areas of accumulation.
As used herein, unless stated otherwise, room temperature is 25° C. And, standard temperature and pressure is 25° C. and 1 atmosphere. As used herein, unless stated otherwise, generally, the term “about” is meant to encompass a variance or range of ±10%, the experimental or instrument error associated with obtaining the stated value, and preferably the larger of these.